Rechargeable battery

ABSTRACT

In a rechargeable battery in which an electrode plate group ( 10 ) obtained by superimposing a positive electrode plate ( 1 ), in which positive electrode material ( 1   a ) is attached to a positive electrode current collector ( 1   b ), and a negative electrode plate ( 2 ), in which negative electrode material ( 2   a ) is attached to a negative electrode current collector ( 2   b ), with a separator ( 3 ) therebetween is accommodated in a battery container ( 4 ) together with electrolyte, the current collectors ( 1   b   , 2   b ) of the electrode plates ( 1, 2 ) are respectively projected at opposite ends of the electrode plate group ( 10 ), forming by themselves flat planes ( 11, 12 ) by being pressed, and current collecting plates ( 8, 9 ) are joined to these flat planes ( 11, 12 ).

TECHNICAL FIELD

[0001] The present invention relates to rechargeable batteries, and inparticular to rechargeable batteries wherein an electrode plate groupobtained by superimposing a positive electrode plate, in which positiveelectrode material is attached to a current collector, onto a negativeelectrode plate, in which negative electrode material is attached to acurrent collector, with a separator therebetween, is accommodated in abattery container together with electrolyte.

BACKGROUND ART

[0002] In recent years, there has been rapid progress in reducing thesize and weight of electronic equipment, which has increased demands toreduce the size and weight and increase the capacity of the batteriesused as their power sources.

[0003] To meet these demands, lithium ion rechargeable batteriesemploying a carbon-based material as the negative electrode activematerial and a transition metal oxide containing lithium, such asLiCoO₂, as the positive electrode active material have been put intopractice by various companies. Lithium rechargeable batteries in whichmetallic lithium or lithium alloy is employed as the negative electrodeactive material had the problem that the lithium precipitated on thenegative electrode as charging proceeded. On the other hand, lithium ionrechargeable batteries are free of such problem and so have excellentcycle characteristics. As a result, there has been vigorous developmentof lithium ion rechargeable batteries and their use in electronicequipment has become more common.

[0004] Lithium rechargeable batteries are studied also as a means forsolving global environmental problems or energy problems. As a way ofguaranteeing power stability while maintaining a good globalenvironment, implementation of technology for load equalization isdesired; considerable benefits in terms of load equalization could beexpected if use of small-scale battery power storage devices capable ofstoring power during the night could be made common in ordinaryhouseholds etc. In order to prevent atmospheric pollution by car exhaustgases and global warming due to CO₂, it would also be desirable toextend the use of electric vehicles in which some or all of the motivepower is obtained by rechargeable batteries. Large lithium ionrechargeable batteries with a cell capacity of about 100 Ah aretherefore being developed for use as battery power storage devices fordomestic use and as power sources for electric vehicles.

[0005] The construction of such a lithium ion rechargeable battery isshown in FIG. 5. An electrode plate group 30 constituted bysuperimposing a positive electrode plate 21, in which positive electrodematerial 21 a is attached to a positive electrode current collector 21b, and a negative electrode plate 22, in which negative electrodematerial 22 a is attached to a negative electrode current collector 22b, wound in spiral fashion with a separator 23 therebetween areaccommodated in a battery container 24 comprising a battery case 25 anda battery closure 26 together with electrolyte. A positive electrodecurrent collector tab 28 with one end joined to a suitable location ofthe positive electrode current collector 21 b has its other endconnected to the inner surface of the battery closure 26 constitutingthe positive electrode terminal, while a negative electrode currentcollector tab 29 with one end joined to a suitable location of thenegative electrode current collector 22 b has its other end connected tothe inside bottom surface of the battery case 25 constituting thenegative electrode terminal. An insulating packing 27 is interposedbetween the inner circumference of the top end aperture of the batterycase 25 and the outer circumference of the battery closure 26 so as tomutually insulate the battery case 25 and the battery closure 26 and toseal the battery container 24.

[0006] However, since current was extracted from a single location of apositive electrode plate 21 and a negative electrode plate 22 throughcurrent collecting tabs 28 and 29 in this structure, the averagedistance from the positive electrode plate 21 and negative electrodeplate 22 to the current collecting tabs 28 and 29 was long. Moreover,the area of current collecting tabs 28 and 29 was small, so theirelectrical resistance was large and the current collecting efficiencywas poor. Furthermore, since the current collecting efficiency was poor,there was the problem that charging and discharging with large currentsresulted in increased battery temperatures, which shortens the life ofthe rechargeable battery.

[0007] Laid-open Japanese Patent Application No. 8-115744, for example,discloses an electrode plate group which is directed to solve theseproblems. In this electrode plate group, current collectors arerespectively projected at one side of the electrode plates, withrespective leads being attached to the leading ends of these projectedportions of the current collectors. Therefore when the electrode platesare wound in spiral fashion, the leads and the end edges of the currentcollectors respectively form a positive electrode end face and anegative electrode end face at opposite ends of the electrode plategroup. Both terminals are connected to the positive electrode end faceand the negative electrode end face respectively. However, suchstructure is subject to the problem of high cost, since leads arerequired and the manufacturing steps are complicated.

[0008] Laid-open Japanese Patent Application No. 10-21953 discloses anarrangement in which current collectors of both electrode plates projectrespectively on opposite sides and their tips make resilient pressurecontact with the positive electrode terminal and negative electrodeterminal. However, the connection between the current collectors and theterminals is only effected by the elastic restoring force of the tips ofthe current collectors, which are bent at an acute angle within acertain range of elasticity. Therefore, the electrical connection isunstable, and the output of the battery also lacks stability underconditions of use in which it is subjected to vibration.

[0009] In view of the above problems of the prior art, an object of thepresent invention is to provide a rechargeable battery wherein theefficiency of current collection is high, the rise in temperature duringcharging/discharging can be reduced, and in which charging/dischargingcan be achieved in a stable fashion with an inexpensive construction.

DISCLOSURE OF THE INVENTION

[0010] A rechargeable battery according to the present inventioncomprises: an electrode plate group including a positive electrodeplate, in which a positive electrode material is attached to a currentcollector, a negative electrode plate, in which a negative electrodematerial is attached to a current collector, the positive and negativeelectrode plates being superimposed with an intervening separatortherebetween, wherein the current collector of one or other of thepositive electrode plate and the negative electrode plate is projectedon at least one side of the electrode plate group for forming by itselfa flat plane on one side of the electrode plate group; an electrolyte; abattery container in which the electrode plate group and the electrolyteare accommodated; and a current collecting plate joined to the flatplane formed at one side of the electrode plate group. Since the currentcollecting plate is joined to the flat plane formed by a side portion ofthe current collectors, the current collection efficiency is high andthe rise in temperature during charging/discharging can be kept small.Furthermore, since the flat plane is formed by the current collectoritself, the construction can be made inexpensive. Moreover, theconstruction is stable with respect to vibration etc since the currentcollecting plate is welded to the flat plane of the current collector,so charging and discharging can be effected in a stable fashion.

[0011] If the positive electrode plate and the negative electrode plateare wound in spiral fashion with the separator interposed therebetween,with their current collectors being respectively projected at oppositeends of the electrode plate group thereby forming respective projectedportions, flat planes can be formed at opposite ends of the electrodeplate group efficiently by pressing the projected portions of thecurrent correctors at opposite ends of the electrode plate group indirections along the winding axis of the electrode plate group.

[0012] The current collecting plate may be arranged in contact with eachof the flat planes and laser-welded in the radial direction at aplurality of locations in the circumferential direction, so that a largenumber of locations of the side edges of the current collectors can beintegrally welded in a simple fashion to the current collecting plates,making it possible to achieve high current collection efficiency with aneasy operation.

[0013] Alternatively, a plurality of ribs may be formed on the currentcollecting plate such as to protrude towards the projected portions ofthe current collectors, the flat planes being formed by pressing theribs against the projected portions of the current collectors, and thecurrent collecting plate being welded to each of the current collectorsat these ribs, so that the current collector plates make reliablecontact with the current collectors at these ribs and they can be weldedtogether even more reliably.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is an axial cross-sectional view of a rechargeable batteryaccording to one embodiment of the present invention;

[0015]FIG. 2 is an axial cross-sectional view of an electrode plategroup in this embodiment in a step wherein a flat plane is formed by theprojected portion of a current collector;

[0016]FIG. 3 is a perspective view of the electrode plate group in thisembodiment in a step in which the current collecting plate is joined tothe flat plane of the current collector;

[0017]FIG. 4 is a perspective view of a modified example of currentcollecting plate in a state welded to the electrode plate group in therechargeable battery according to the present invention; and

[0018]FIG. 5 is an axial cross-sectional view of a rechargeable batteryaccording to an example of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] A lithium ion rechargeable battery according to an embodiment ofthe rechargeable battery of the present invention is described belowwith reference to FIG. 1 to FIG. 3.

[0020] In FIG. 1, reference numeral 1 represents a positive electrodeplate and reference numeral 2 represents a negative electrode plate. Anelectrode plate group 10 is constituted by winding in spiral fashion thepositive electrode plate 1 and the negative electrode plate 2 in amutually opposed condition with a separator 3 made of microporouspolyethylene film therebetween. This electrode plate group 10 isaccommodated within a battery container 4 together with electrolyte. Thebattery container 4 comprises a battery case 5 which is of cylindricalenclosure shape and constitutes an negative electrode terminal, and abattery closure 6 constituting a positive electrode terminal. Aninsulating packing 7 is interposed between the inner circumference ofthe top aperture of the battery case 5 and the outer circumference ofthe battery closure 6, whereby mutual insulation is effectedtherebetween and the battery container 4 is sealed. The separator 3 isinterposed also between the electrode plate group 10 and the innercircumference of the battery case 5.

[0021] The positive electrode plate 1 is constituted by coating bothsurfaces of a positive electrode current collector 1 b with a positiveelectrode material 1 a; a side part (in the example illustrated, the toppart) of this positive electrode current collector 1 b projects from theportion that is coated with the positive electrode material 1 a. Thenegative lectrode plate 2 is constituted by coating both surfaces ofnegative electrode current collector 2 b with a negative electrodematerial 2 a; a side part opposite from the projected portion of thepositive electrode current collector 1 b (in the example illustrated,the bottom part) of this negative electrode current collector 2 bprojects from the portion that is coated with the negative electrodematerial 2 a. The separator 3 projects to the outside beyond both sideedges of the coated portions of the positive electrode plate 1 and thenegative electrode plate 2.

[0022] The side edge of the positive electrode current collector 1 bthat projects further than the separator 3 is elastically deformed byapplying pressure thereto, whereby a flat plane 11 is formed. A positiveelectrode current collecting plate 8 is joined to this flat plane 11.Likewise, the side edge of the negative electrode current collector 2 bthat projects further than the separator 3 is elastically deformed byapplying pressure thereto, whereby a flat plane 12 is formed, and anegative electrode current collecting plate 9 is joined to this flatplane 12. The positive electrode current collecting plate 8 and thenegative electrode current collecting plate 9 are respectively connectedto the battery closure 6 and the battery case 5. Reference numerals 8 aand 9 a respectively denote connecting strips extending from the outercircumference of the current collecting plates 8 and 9 for connectingthem to the inside surface of the battery closure 6 and the insidebottom surface of the battery case 5, respectively.

[0023] A detailed description of the positive electrode plate 1, thenegative electrode plate 2, and the electrolyte will now be given. Thepositive electrode current collector 1 b is made of aluminum foil or thelike. The positive electrode plate 1 is constituted by coating bothsurfaces of the positive electrode current collector 1 b with a positiveelectrode material 1 a containing a positive electrode active materialand a binder. For the positive electrode active material, LiCoO₂,LiMn₂O₄, LiNiO₂, any other lithium oxide in which one of Co, Mn or Ni issubstituted with another transition metal, or a lithium-containingtransition metal oxide other than these may be used. In particular,Mn-based lithium-containing transition metal oxides such as the globallyabundant low-cost LiMn₂O₄ are suitable.

[0024] The negative electrode current collector 2 b is made of copperfoil or the like, and the negative electrode plate 2 is constituted bycoating both surfaces of the negative electrode current collector 2 bwith a negative electrode material 2 a containing a negative electrodeactive material and a binder. For the negative electrode activematerial, carbon-based materials such as graphite, petroleum coke,carbon fiber, or organic polymer sintered products, or metals or oxides,or composite materials of these capable of occluding and releasinglithium, may be used.

[0025] The electrolyte may be obtained by dissolving a lithium salt suchas lithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), orlithium fluoroborate (LiBF₄) into a non-aqueous solvent such as ethylenecarbonate (EC), propylene carbonate (PC), diethylene carbonate (DEC) orethylene methyl carbonate (EMC), either alone or in combination, at aconcentration of 0.5 mol/dm³ to 2 mol/dm³.

[0026] To give a specific example, electrolyzed manganese dioxide (EMD:MnO₂) and lithium carbonate (Li₂CO₃) were mixed at a ratio Li/Mn=1/2 andsintered in the atmosphere of 800° C. for 20 hours, whereby LiMn₂O₄ wasproduced as the positive electrode active material. The positiveelectrode material 1 a was then obtained by mixing, by weight, 92%LiMn₂O₄, 3% acetylene black serving as conducting agent, and 5%polyfluorovinylidene as binder. In order to knead the positive electrodematerial 1 a into the form of a paste, the polyfluorovinylidene servingas the binder was employed in the form of N-methylpyrrolidonedispersion. The mixing ratios given above are ratios in terms of thesolid fractions. Both faces of the positive electrode current collector1 b made of 20 μm thick aluminum foil were coated with this positiveelectrode material paste such that positive electrode material layerswere formed except a region of width 10 mm on one side edge, which wasleft uncoated. The film thickness of both positive electrode materiallayers was the same and the sum of the two film thicknesses aftercoating and drying was 280 μm, giving a positive electrode platethickness of 300 μm. After this, the positive electrode plate 1 wascompressed using a press roll of diameter 300 mm, to reduce thethickness of the positive electrode plate 1 to 200 μm. The density ofthe positive electrode material was then 3.0 g/cm³.

[0027] For the negative electrode material 2 a, a mixture of artificialgraphite and styrene butadiene rubber (SBR) as a binder in a weightratio of 97:3 was employed. In order to knead the negative electrodematerial 2 a into the form of a paste, the styrene butadiene rubberbinder was employed in the form of an aqueous dispersion. The abovemixing ratios are expressed as solid fractions. Both faces of thenegative electrode current collector 2 b made of 14 pm thick copper foilwere coated with this negative electrode material paste such thatnegative electrode material layers were formed except a region of width10 mm on one side edge, which was left uncoated. After this, thenegative electrode plate 2 was compressed using a press roll of diameter300 mm, to reduce the thickness of the negative electrode plate 2 to 170μm. The density of the negative electrode material was then 1.4 g/cm³.

[0028] The electrolyte was obtained by dissolving lithiumhexafluorophosphate (LiPF₆) as solute in a concentration of 1 mol/dm³ ina solvent obtained by mixing ethylene carbonate (EC) and diethylenecarbonate (DEC) in a volume blending ratio of 1:1.

[0029] These positive electrode plate 1 and negative electrode plate 2thus produced are opposed to each other with an intervening separator 3therebetween and wound around in spiral fashion to form an electrodeplate group 10, in such a manner that the portions of the currentcollectors 1 b, 2 b which were left uncoated project at opposite ends ofthe electrode plate group 10. This electrode plate group 10 is insertedand arranged in position in a molding jig 13 of cylindrical enclosureshape as shown in FIG. 2, and is subjected to pressure by a pressingmember 14 from one end aperture of the molding jig 13. Thereby, theprojected portions of the current collectors 1 b, 2 b are elasticallydeformed to be bent radially inwards substantially at 90° as shown bythe phantom lines, whereby flat planes 11, 12 are formed at oppositeends of the electrode plate group. Since the positive electrode plate 1and the negative electrode plate 2 are wound in spiral fashion, theprojected portions of the current collectors 1 b, 2 b are not bentradially outwards. Rather, all of the projected portions of the currentcollectors are uniformly and progressively bent radially inwards. As aresult, although folding may occur to some extent, they are as a wholedeformed together into flat planes 11, 12.

[0030] Next, the electrode plate group 10 formed with flat planes 11, 12is removed from the molding jig 13 and, as shown in FIG. 3, the currentcollecting plates 8, 9 are pressed into contact with the flat planes 11,12, and these are laser welded together by irradiating a plurality oflocations in the circumferential direction of the surfaces of thecurrent collecting plates 8, 9 with a laser beam 15 in radial fashionfrom the middle towards the outer periphery. After this, the electrodeplate group 10 with these current collecting plates 8, 9 joined theretois accommodated within the battery case 5 and vacuum-impregnated withthe electrolyte. The current collecting plates 8, 9 are connected bylaser welding etc to the battery closure 6 and the battery case 5,respectively, and the battery case 5 is sealed with the battery closure6.

[0031] As described above, the electrode plate group 10 in this lithiumion rechargeable battery is constituted by winding in spiral fashion apositive electrode plate 1 and a negative electrode plate 2 with aseparator 3 therebetween, such that the current collectors 1 b, 2 b ofthe two electrode plates respectively project at opposite ends thereofand the current collecting plates 8, 9 are joined to the flat planes 11,12 formed by the projected portions of the current collectors 1 b, 2 b.Accordingly, the efficiency of current collection is high and the risein temperature during charging/discharging can be kept small.Furthermore, since the flat planes 11, 12 are formed by the currentcollectors 1 b, 2 b themselves, the construction can be made of lowcost. Furthermore, the construction is stable with respect to vibrationetc, because these flat planes 11, 12 are welded to the currentcollecting plates 8, 9, so charging and discharging can be effected in astable fashion.

[0032] Since.the flat planes 11, 12 for joining the current collectingplates 8, 9 are formed by applying pressure to both ends of theelectrode plate group 10 in the direction along the core of the windingaxis, they can be formed efficiently.

[0033] The current collecting plates 8, 9 are pressed towards the flatplanes 11, 12 and subjected to laser welding in the radial direction ata plurality of locations in the circumferential direction in thistightly pressed condition. Therefore, integral welding of a large numberof locations of the side edges of the current collectors 1 b, 2 b to thecurrent collecting plates 8, 9 can be achieved in a straightforwardfashion, enabling high current collection efficiency to be achieved withease of operation.

[0034] In the description of the above embodiment, an example was givenin which the entire surface of the current collecting plates 8, 9 was offlat plate shape. FIG. 4 illustrates a modified example of a currentcollecting plate 8 or 9, in which a plurality of ribs 16 are formedprojecting towards the projected portions of the current collectors 1 b,2 b of the electrode plate group 10 in radial fashion. Laser welding iseffected along these ribs 16 under a condition in which the currentcollecting plates 8, 9 are pressed toward the electrode plate group 10such that these ribs 16 bite into the projected portions of the currentcollectors 1 b, 2 b so as to form the flat planes 11, 12.

[0035] If such ribs 16 are provided on the current collecting plates 8,9 and laser welding is conducted with these being pressed against theprojected portions of the current collectors 1 b, 2 b, the flat planes11, 12 formed by the projected portions make reliable contact with thecurrent collecting plates 8, 9 through the ribs 16, whereby the currentcollecting plates 8, 9 and the current collectors 1 b, 2 b can be weldedtogether even more reliably.

INDUSTRIAL APPLICABILITY

[0036] As will be clear from the above description, with therechargeable battery of the present invention, the current collector ofone or other of the electrodes projects on at least one side of theelectrode plate group, a flat plane being formed at the tip of thisprojected portion by itself, and a current collector plate is welded tothis projected portion of the current collector. Accordingly, thecurrent collection efficiency is high and the rise in temperature duringcharging/discharging can be made small. Since the flat plane is formedby the current collector itself, an inexpensive construction can beachieved, and since the current collecting plate is joined to the flatplane, the construction is stable with regard to vibration etc. Thepresent invention thereby realizes an inexpensive structure forelectrode plate group with which the battery exhibits excellent currentcollection efficiency and stable charging/discharging characteristics.

1-4. (Canceled)
 5. A method of manufacturing a rechargeable battery,comprising the steps of: interposing a separator between a positiveelectrode plate and a negative electrode plate to form a multilayerelectrode structure, said positive electrode plate and said negativeelectrode plate including uncoated end portions; winding said multilayerelectrode structure in spiral fashion to form an electrode plate grouphaving a spiral configuration, said positive electrode plate, saidnegative electrode plate and said separator being positioned relativeone another prior to the winding of said multilayer structure such thatafter being wound the uncoated end portions of said positive electrodeplate and said negative electrode plate extend respectively fromopposite ends of the electrode plate group thereby defining uncoatedprojected portions; contacting a one of the opposite ends of theelectrode plate group with at least one current collecting plate havinga plurality of ribs which extend radially and project towards theuncoated projected portions; and pressing the at least one currentcollecting plate toward the electrode plate group such that the ribsbite into the uncoated projected portions in contact area portionscorrespondingly located.
 6. The method of manufacturing a rechargeablebattery according to claim 5, further comprising the step of welding theat least one current collecting plate to the electrode plate group at aplurality of locations within the contact area portions to form aelectrode plate group assembly.
 7. The method of manufacturing arechargeable battery according to claim 6, wherein the at least onecurrent collecting plate includes a positive current collecting plateand a negative current collecting plate, said step of welding includingwelding the positive and negative current collecting plates onrespective ones of the opposite ends of the electrode plate groupcorresponding to the positions of the uncoated projected portions of thepositive electrode plate and the negative electrode plate to form theelectrode plate group assembly.
 8. The method of manufacturing arechargeable battery according to claim 7, further comprising the stepsof: accommodating said electrode plate group assembly in a battery case;and vacuum-impregnating the electrode plate group assembly within thebattery case with an electrolyte.
 9. The method of manufacturing arechargeable battery according to claim 8, further comprising the stepsof: connecting the current collecting plates each to a respective one ofa battery closure and the battery case; and sealing the battery casewith the battery closure.
 10. The method of manufacturing a rechargeablebattery according to claim 5, wherein each of the plurality of ribsincludes a flat region at an apex thereof which, when the ribs arepressed into the the uncoated projected portions in the contact areaportions, the uncoated projected portions are deformed into flattenedareas in the contact area portions, surfaces of which extend generallyorthogonal to the winding axis.
 11. The method of manufacturing arechargeable battery according to claim 6, further comprising the stepof welding the at least one current collecting plate to the electrodeplate group at a plurality of locations within the flattened areas toform an electrode plate group assembly.
 12. The method of manufacturinga rechargeable battery according to claim 11, wherein the at least onecurrent collecting plate includes a positive current collecting plateand a negative current collecting plate, said step of welding includingwelding the positive and negative current collecting plates onrespective ones of the opposite ends of the electrode plate groupcorresponding to the positions of the uncoated projected portions of thepositive electrode plate and the negative electrode plate to form theelectrode plate group assembly.
 13. The method of manufacturing arechargeable battery according to claim 12, further comprising the stepsof: accommodating said electrode plate group assembly in a battery case;and vacuum-impregnating the electrode plate group assembly within thebattery case with an electrolyte.
 14. The methos of the manufacturing arechargeable battery according to claim 13, further comprising the stepsof: connecting the current collecting plates each to a respective one ofa battery closure and the battery case; and sealing the battery casewith the battery closure.